This invention is related to semiconductor laser devices and, more particularly to semiconductor laser devices with replaceable laser diode bars.
A number of lasers, such as slab and rod lasers, are designed to produce output pulses having a high average output power, such as 1,000 W-10,000 W, operating either continuously or in a repetitively pulsed mode. High levels of output power are required in a number of applications including laser radar, mine detection, welding, material processing, surface coating, isotope separation and x-ray lithography, among others. In order to obtain such high power levels, a primary laser, such as a slab or a rod laser, can be pumped by a laser pump source, such as an array of semiconductor laser diodes. The laser pump source must also operate at relatively high power levels and either at relatively high pulse repetition rates or continuously in order to generate the necessary power to excite the primary laser.
Semiconductor lasers that pump a primary laser are typically made of multiple linear arrays of laser diodes, also known as linear laser diode bars. The linear laser diode bars are then arranged in a two-dimensional laser diode array. To form the two-dimensional laser diode array, the linear laser diode bars are typically soldered on microchannel heat sinks, which are subsequently stacked. The two-dimensional laser diode array is capable of generating high intensity light for pumping the primary laser.
Although the soldered two-dimensional laser diode array design is suitable for laser applications, it creates significant difficulty when individual linear laser diode bars must be replaced. The linear laser diode bars occasionally fail for a variety of reasons, such as facet erosion (also called xe2x80x9cspewingxe2x80x9d), solder bonding failure, overheating, dark line defect growth, and gradual degradation, and must be replaced. Because the linear laser diode bars are soldered on heat sinks, however, the bars cannot be easily removed and reinserted. Instead, the entire two-dimensional laser diode array must either be scrapped or, if a repair is to be attempted, the entire array typically must be disassembled by breaking the solder joints, if possible, replacing the failed bar, and reassembling the array by resoldering the new laser diode bar into position, then resoldering the array together. Because of the difficulty involved in breaking the solder joints and resoldering the array, the replacement of conventional linear laser diode bars cannot be performed by a typical user of a semiconductor laser device. In fact, the replacement process typically cannot even occur at or near the location at which the semiconductor laser device is deployed. Instead, the semiconductor laser device should be returned to its manufacturer or a maintenance depot for repair, which can take weeks. Thus, the semiconductor laser device is inoperable and unavailable during the time it is being repaired and during the time it is in transit to and from the manufacturer.
Replacing a linear laser diode bar in a two-dimensional laser diode array, therefore, can be costly to users of the semiconductor laser devices who must be without the device for weeks while it is being repaired. In addition, it is costly and labor-intensive for the manufacturers of such semiconductor laser devices or for other maintenance personnel to make the repairs necessary when a linear laser diode bar must be replaced. As such, there is a need in the industry to provide a two-dimensional laser diode array for use in semiconductor laser devices, in which the individual linear laser diode bars may be easily and immediately replaced without having to disassemble the entire array and without a significant investment of time and/or money.
Thermal heat dissipation is another concern for semiconductor lasers. In this regard, in generating pulses having a relatively high average output power and a relatively high repetition rate, the laser pump source generates a significant amount of heat, which elevates the temperature of the laser pump source in the absence of external cooling. For example, the heat generated by a laser can be approximated by the difference between the power input to the laser and the output power received from the laser. Typically, the heat generated by a conventional laser pump source is approximately 45%-60% of the input power, with the overall efficiency of a solid state laser comprised of a laser pump source and a downstream laser system being about 10%-20%.
Lasers, such as semiconductor laser diode arrays, however, typically have a maximum operating temperature above which the operation of the laser can be unreliable. In addition, operation of a laser, such as a semiconductor laser diode array, at an elevated temperature generally reduces the effective lifetime of the laser even though such temperatures may be below the maximum operating temperature. For example, operation of a semiconductor laser diode array at an elevated temperature can damage the emitting facet of the laser diode array, thereby impairing its performance.
One type of semiconductor laser diode array that provides suitable cooling during laser operation, while also being economical to produce compared to other semiconductor laser diode arrays, is the immersion cooled array. An immersion cooled array is made from linear laser diode bars mounted on microchannel coolers. The simple linear laser diode bars are capable of continuous wave (CW) or high duty factor operation by clamping the bars to liquid cooled heat sinks, and immersing the entire two-dimensional laser diode array in a flowing dielectric coolant. Details of the immersion cooled array are included in U.S. Pat. No. 5,495,490, which is incorporated herein by reference.
Because of the time and expense involved in replacing individual linear laser diode bars in conventional laser diode arrays, it would be advantageous to be able to quickly and easily replace individual linear laser diode bars in laser diode arrays. In particular, there is a need in the industry to utilize two-dimensional laser diode arrays, such as immersion cooled arrays, in semiconductor laser diode devices, in which the arrays include individual linear laser diode bars that are easily and immediately replaceable without a significant investment of time and/or money. Furthermore, due to the efficient and economical nature of the immersion cooled array, it would be desirable to be able to utilize such an immersion cooled two-dimensional laser diode array made from removable linear laser diode bars in a variety of applications.
The laser diode arrays with removable linear laser diode bars and the methods of removing and replacing linear laser diode bars of the present invention provide easy and immediate removal of individual linear laser diode bars in laser diode arrays. Therefore, the individual linear laser diode bars may be removed and replaced in the field without having to transport the laser diode array to a maintenance depot or the like, which significantly reduces the time and labor involved in the removal and replacement, as compared to conventional removal and replacement techniques. In addition, the removable linear laser diode bars may be utilized with various types of laser diode arrays, including efficient and economical immersion cooled laser diode arrays.
One embodiment of the method for removing at least one of a plurality of removable linear laser diode bars from a laser diode array includes accessing a removable linear laser diode bar within the laser diode array and slideably removing the removable linear laser diode bar, such as upon failure of the linear laser diode bar. The laser diode array is at least partially made of the plurality of removable linear laser diode bars and a plurality of spacers, such that each removable linear laser diode bar is disposed between a respective pair of spacers. As such, when the removable linear laser diode bar is slideably removed from the laser diode array, it is slideably removed from between the respective pair of spacers in the laser diode array. In addition, the removable linear laser diode bar is slideably removed without breaking any mechanical connection between the removable linear laser diode bar and the respective pair of spacers.
To slideably remove the removable linear laser diode bar from between the respective pair of spacers, a force may be applied to the removable linear laser diode bar in a direction away from the plurality of spacers. The force, therefore, overcomes the frictional force between the removable linear laser diode bar and the respective pair of spacers.
The laser diode array may be immersion cooled. The immersion cooled laser diode array includes a plurality of removable linear laser diode bars, a plurality of spacers, and a liquid coolant flowing about and through the immersion cooled laser diode array. As before, each removable linear laser diode bar is disposed between a pair of spacers. Replacing a removable linear laser diode bar includes at least partially draining the liquid coolant from the immersion cooled laser diode array. The removable linear laser diode bar is then accessed, which may involve opening a housing in which the removable linear laser diode bars are disposed. The removable linear laser diode bar is slideably removed from between the respective pair of spacers in the array, and a replacement linear laser diode bar is slideably inserted between the respective pair of spacers.
Slideably removing the respective removable linear laser diode bar may involve removing the bar without breaking a mechanical connection between the respective removable linear laser diode bar and the respective pair of spacers. Likewise, slideably inserting the replacement linear laser diode bar may involve positioning the replacement linear laser diode bar between the respective pair of spacers without forming a mechanical connection between the replacement linear laser diode bar and the respective pair of spacers. For example, in one embodiment of the present invention, the replacement linear laser diode bar is secured between the respective pair of spacers with frictional forces. After slideably inserting the replacement linear laser diode bar, a liquid coolant may be introduced about and through the laser diode array for immersion cooling.
In addition to the methods for removing and replacing linear laser diode bars in laser diode arrays, another aspect of the present invention also includes a laser diode assembly with such removable linear laser diode bars. The laser diode assembly comprises a two-dimensional laser diode array that includes a plurality of linear laser diode arrays, each of which has first and second major surfaces. First and second electrodes are electrically connected to the two-dimensional laser diode array for supplying the array with electrical energy, such that at least one of the linear laser diode arrays is capable of emitting a laser output from its emitting facet. At least one heat sink of a plurality of heatsinks is in thermal communication with each linear laser diode array to form a plurality of removable linear laser diode bars. The laser diode assembly also includes a plurality of spacers in a predetermined spaced apart relationship with one another. As such, each removable linear laser diode bar is slideably insertable and sideably removable between a respective pair of spacers. For instance, in one embodiment of the laser diode assembly of the present invention, the removable linear laser diode bar may be secured between the respective pair of spacers with frictional forces.
The spacers may extend from a first end rearwardly to a second end and the laser diode assembly may also include an electrically insulating element to which the second end of each spacer is fixed in order to electrically isolate the spacers. In other embodiments, a plurality of electrically insulating sheets may be disposed between respective pairs of spacers to electrically isolate the spacers.
The two-dimensional laser diode array, the first and second electrodes, the plurality of heat sinks, and the plurality of spacers may be disposed in a housing. A window may be located in the front surface of the housing, such that the respective emitting facets of the plurality of linear laser diode arrays are positioned adjacent the window. In this embodiment of the laser diode assembly of the present invention, the laser diode array may be immersion cooled by positioning the plurality of linear laser diode arrays adjacent the window in a predetermined spaced apart relationship such that liquid coolant flows between the window and the linear laser diode arrays. The housing also may define inlet and outlet ports through which the liquid coolant flows into and out of the housing.
The heat sinks may extend rearwardly from the plurality of linear laser diode arrays, and first channels may be defined between the rearwardly extending heat sinks. The first channels can, therefore, receive the liquid coolant such that the liquid coolant directly contacts and cools the linear laser diode arrays by immersion while maintaining electrical isolation between the first and second electrodes. The first channels may be further defined by disposing a first end of each heat sink on one of the first and second major surfaces of a linear laser diode array. Each heat sink may extend rearwardly to a second end, and electrically insulating members may be disposed between the respective second ends of a pair of heat sinks of each removable linear laser diode bar, which further defines the first channels between the pair of heat sinks, the electrically insulating members and the linear laser diode arrays.
Additionally, second channels may be defined between the removable linear laser diode bars that extend forwardly from the plurality of electrically isolated spacers, when the removable linear laser diode bars are inserted between respective pairs of spacers. The second channels can also receive liquid coolant such that the liquid coolant directly contacts and cools the removable linear laser diode bars by immersion while maintaining electrical isolation between the first and second electrodes.
In a further embodiment of the laser diode assembly of the present invention, the two-dimensional laser diode array, the first and second electrodes, the heat sinks, and the spacers are disposed in the housing, and a solid state laser is disposed in an opening in the front surface of the housing. Thus, the two-dimensional laser diode array is disposed within the housing such that the respective emitting facets of the laser diode arrays are positioned adjacent the solid state laser in a predetermined spaced apart and aligned relationship, such that the laser diode array pumps the solid state laser. The laser diode array of this embodiment may be immersion cooled by positioning the linear laser diode arrays adjacent the solid state laser such that liquid coolant flows between the solid state laser and the linear laser diode arrays, which cools both the solid state laser and the linear laser diode arrays.
The laser diode assembly with removable linear laser diode bars and the methods of removing and replacing linear laser diode bars of the present invention provide easy and immediate removal of individual linear laser diode bars in laser diode arrays. As such, the cost and labor involved in removing and replacing individual linear laser diode bars is significantly reduced, as compared to conventional techniques. In addition, the laser diode assembly of the present invention functions at least as well and at least as efficiently as conventional laser diode arrays, particularly in instances in which the laser diode assembly of the present invention is immersion cooled.